Killer Sudoku Strategy: 7 Techniques

1. Learn the unique combinations

Some cages can only be made one way. Two cells: 3 = 1+2, 4 = 1+3, 16 = 7+9, 17 = 8+9. Three cells: 6 = 1+2+3, 7 = 1+2+4, 23 = 6+8+9, 24 = 7+8+9. Write those digits in as notes straight away.

2. Rule out impossible digits

A two-cell cage of 5 can't contain 5 or anything above 4. A two-cell cage of 15 can only use 6 to 9. Big numbers and small numbers tell you a lot.

3. The 45 rule: innies

Add up the cages lying wholly inside a box. If one cell of the box is left over (it belongs to a cage that sticks out), its digit is 45 minus that total.

4. The 45 rule: outies

Add up every cage that touches a box. The total is more than 45 because some cells stick out of the box. The cells outside the box (the outies) add up to the difference.

5. Use several rows at once

Two rows add up to 90, three to 135. A band of three boxes often has just one or two cells left over by whole cages.

6. Normal sudoku still applies

Once a few digits are in, use the usual singles and pairs. Cages give extra help: a pair of digits locked in a cage inside one box can't be anywhere else in that box.

7. Keep notes tidy

Write the possible combinations as notes in each cage. Erase as you rule digits out. Use the hint if you get stuck.

Last updated 2026-10-19